This invention relates to radial piston pumps and more particularly to an improved radial piston pump construction for reducing vibrations accompanying pump operation.
Radial piston pumps of the type having spring loaded plungers displaced by an eccentric to effect unidirectional flow of fluid through openings in the plunger walls from chambers internally of the plungers to surge chambers externally of the plungers, are already known as disclosed, for example, in German Pat. Nos. OS 2,243,138 and AS 2,061,960. Such pumps advantageously operate to limit flow through intake restrictors and also reduce pump torque, that otherwise increases with pump speed, to conserve output generated energy. However, such pumps have the disadvantage of operating with a high degree of non-uniform rate of fluid supply to the fluid consuming devices or systems being serviced by the pump. Correspondingly high pressure pulsations result from such operation producing a disturbing effect. If, for example, such a pump is used for supply of fluid to an auxiliary power steering system, the pressure pulsations are felt by the driver of a vehicle on the hand steering wheel. Further, the compressional vibrations produced by such pressure pulsations create noise which often exceeds tolerable levels. If other fluid pressure consumers such as level regulators and braking systems are supplied with pressure fluid, a pressure fluid reservoir is then utilized as disclosed for example, in U.S. Pat. No. 4,012,993. The pressure reservoir in such case serves to store pressure fluid during periods of lower consumption to insure full operation of all fluid systems at all times. The pressure reservoir inserted between the pump and the fluid pressure systems also acts as a vibration dampener so as to reduce the transfer of such vibrations. Such pressure reservoir may, however, affect only compressional vibrations within a limited operating pressure range and at low frequencies. For compressional vibrations within a wide pressure range of 0 to 130 BAR and between pump speeds of 600 to 6,000 rpm applicable to a suction regulated radial piston pump for auxiliary power steering systems, the foregoing vibration reducing measures will be very costly and yet inadequate.
It is therefore an important object of the present invention to reduce non-uniform flow caused by high flow rate pulsations in the fluid supply stream and resulting noise from a radial piston pump by means of a low cost constructional modification so that such pump may be used without vibration suppressors for auxiliary power steering systems, for example.